In a radio communication system (LTE system) that complies with LTE (Long Term Evolution) with its standards currently being discussed in 3GPP (Third Generation Partnership Project), a radio base station assigns a radio resource in radio communication between the radio base station and a radio terminal (for example, see Non Patent Literature 1).
Further, in an LTE system according to a Time Division Duplex (TDD) scheme (hereinafter, referred to as “TD-LTE system”), in order to increase a frequency utilization efficiency and improve quality of radio communication, it is considered that adaptive array control using an array antenna is introduced to the radio base station.
The adaptive array control includes a beamforming in which the peak of a directivity pattern of the array antenna is oriented to a radio terminal subordinate to the radio base station and a null steering in which the null of the directivity pattern of the array antenna is oriented to a radio terminal subordinate to another radio base station.
Further, in the LTE system, in order to ensure the reliability of the radio communication, Hybrid Automatic Repeat reQuest (HARQ), which is one of the automatic repeat requests, is introduced.